The use of unmanned aerial vehicles, commonly identified as UAVs, and identified by the United States Federal Aviation Administration (FAA) and international authorities as unmanned aircraft systems (UAS), has increased significantly in the last decade. A UAV is a powered aerial vehicle that does not carry a human operator, but may carry a wide range of a variety of sensing and communication devices, weapons of many kinds, cargo, and, rarely, people. There are, at present, many different available and proposed designs of UAVs. Some are programmed to fly autonomously, while others are piloted remotely. There are UAVs that are recovered for reuse and UAVs that are used for only a single operation, as well as UAVs that carry lethal or nonlethal payloads. Payloads can include everything from munitions to aerial surveillance equipment and the like. UAVs can range in size from the Micro Air Vehicles that weigh less than a pound to large aircraft that weigh more than 40,000 pounds and in cost from a few thousand U.S. dollars to tens of millions of U.S. dollars.
Although military applications account for the greatest usage of UAVs, an increasing number of civilian applications, such as, for example, conducting commercial aerial surveillance, performing geochemical, geophysical and geomagnetic surveys in connection with oil, gas, and mineral exploration and production, search and rescue missions, and remote environmental sensing, can also be conducted with the use of UAVs. A UAV may be used effectively and is increasingly preferred for both civilian and military missions or operations deemed too dangerous for humans to undertake in more conventional aerial vehicles, such as the attack and reconnaissance missions currently conducted by military UAVs. Single use UAVs, common in military applications, can also be useful for civilian applications.
Unlike a missile, a UAV is capable of controlled, sustained level flight and is powered by an engine, typically a jet engine, a reciprocating engine, or another type of propulsion system. While most UAVs are fixed wing aircraft, some employ rotors, or are hybrids with both fixed wings and rotors. The ability to take off and land vertically can increase the usefulness of a UAV. The range, altitude, speed, and endurance capabilities can vary widely for different types of UAVs, as can the degree of autonomous operation. UAVs are no longer likely to be only remotely controlled or remotely piloted, but, in addition, have sophisticated automated built-in control and/or guidance systems. Such systems are able to perform functions like speed and flight path stabilization and navigation. These control and/or guidance systems may also perform one or all of such functions as combining information from different sensors, coordinating communication in the presence of incomplete or imperfect information, determining an optimal path in accordance with objectives and/or constraints, and other required control strategies. An unmanned aerial system (UAS) that includes at least one UAV will also include one or more ground control stations, specialized data control links, and other related support equipment, such as, for example, the same control systems used in aerial and space applications.
Most unmanned aerial vehicles are provided with landing structures that may or may not include wheels capable of moving the UAV on the ground. Vertical take off and landing (VTOL) UAVs may be less likely to move on the ground between landing and take off and, therefore, are less likely to have wheels, but some VTOL UAVs do have wheels. Fixed wing UAVs, which are more likely to have wheels, presently require some kind of flat runway surface for wheeled take offs and landings. Currently neither VTOL nor fixed wing UAVs equipped with wheels are expected to move for very long distances on the ground and, as a result are capable of only very limited ground movement or ground transit. When wheeled UAVs must move on the ground, their movement is typically powered by the UAV's motive power source, which is usually some type of internal combustion engine that uses a standard aircraft or hybrid type of fuel. A conceptual VTOL type of UAV designed to conform to U.S. Air Force Special Operations Transport requirements that is capable of ground transit has been proposed by AirShip Technologies Group (www.AirShipTG.org). This proposed UAV will use an electric motor in-wheel drive train employing lithium-ion electric battery driven motors and a drive-by-wire system that will enable the driver to maneuver the wheels during ground movement. This system, which has not been built, appears intended to move a UAV only short distances on the ground, and its ability to improve UAV ground movement has not been demonstrated. The description of this vehicle, moreover, does not suggest how the improvements in ground travel and stealth achieved by the present invention could be produced.
A ram wing ground effect vehicle capable of limited flight that includes an undercarriage with wheels and an internal combustion engine driving a generator used to power electric motors at each wheel and a ducted fan to enable ground movement is described in U.S. Pat. No. 5,860,620 to Wainfan et al. This arrangement allows the vehicle to move on the ground under battery power for short distances and gives the vehicle low acoustic and infrared (IR) signatures. Neither of the aforementioned vehicles, however, has been designed to travel in contact with a ground surface for an extended time period. Ground travel capability in these vehicles is significantly limited by available battery power, and it is not suggested either how or whether ground travel capability could or should be improved or enhanced in any way.
Moving a commercial aircraft on the ground during taxi by means other than the aircraft's main engines or turbines has been described in the art. In U.S. Pat. No. 7,445,178 to McCoskey et al and U.S. Pat. No. 7,226,018 to Sullivan, for example, systems able to move aircraft on the ground during taxi using wheel motors are described. U.S. Pat. Nos. 7,975,960 and 8,220,740 to Cox et al, owned in common with the present application, describe a nose wheel control apparatus capable of driving a taxiing aircraft independently on the ground. None of the foregoing art, however, suggests employing the devices or systems described therein in connection with an unmanned aerial vehicle to enhance the independent ground travel capability of a UAV or to enhance stealth in a UAV or any other type of aircraft.
The prior art, therefore, has not provided a method or system for improving ground travel capability in unmanned aerial vehicles or for enhancing stealth in UAVs and other aircraft.